Case Studies: Solving Pressure Distribution Problems

A manufacturer and supplier of load cells and torque and pressure sensors solved fluctuations in clamping pressure during manufacture in part through the use of a pressure-recording film.

The clamping pressure used to bond Futek’s metal foil strain gage to the transducer body was not initially uniform. Source: Sensor Products Inc.

Futek (Irvine, CA), manufacturer and supplier of load cells and torque and pressure sensors, experienced difficulty assembling some of its load cells to specification. By performing several tests, and controlling different variables, the company found fluctuations in clamping pressure to be a significant factor.

Futek’s sensors incorporate metal foil strain gage technology. The adhesive the company uses to bond the gages to sensors requires a clamping pressure of 50 to 75 psi. However, by using Pressurex from Sensor Products Inc. (Madison, NJ) Futek was able to see that the pressure fluctuated from 50 psi to upwards of 200 psi in some of its production runs.

Pressurex is a thin flexible film that easily and rapidly shows inconsistencies in surface pressure between mating and contacting surfaces.

This discovery led Futek to use Pressurex to help redesign several of its clamps to incorporate silicone die springs to regulate the pressure more precisely. “A sample pack of Pressurex with film that revealed different surface pressure ranges allowed our production to continue,” says James Meiselbach, a mechanical engineer at Futek.

Meiselbach found using Pressurex to be a simple procedure. To measure the surface pressure of a clamp around the outside of a load cell, he cut Pressurex in the configuration of the clamp surface area, placed it in between the clamp and the load cell, applied force, unclamped it, and removed the Pressurex. He then compared the film, which changes color depending on how much pressure is exerted, to an accompanying color calibration chart.

Meiselbach became aware of Pressurex while working for an aerospace company. “We were having a problem with the main rotor blade of a helicopter. Interference was causing a fatigue crack in one of the inner spar tubes of the rotor blade,” says Meiselbach. “We put a large sheet of Pressurex in the bonding tool, bagged it up and pressurized it in the autoclave. When we removed the film, we were able to identify the exact amount of pressure causing the crack.”

Sensor Products Inc.(973) 884-1755www.sensorprod.com

Benefits

Pressurex film allowed Futek to see that pressure fluctuated from 50 psi to upwards of 200 psi in some of its production runs.

This discovery led Futek to use Pressurex to help redesign several of its clamps to incorporate silicone die springs to regulate the pressure more precisely.

Pressurex reveals surface pressure from 2 to 43,200 psi.

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